The present invention relates to an optical recording disk, and more particularly to an optical recording disk comprising a light transmissive substrate, a recording film disposed on the substrate directly or through an intermediate layer, and a protection layer disposed on the recording film, and a process for producing such an optical recording disk.
Hitherto, there has been known, e.g., a photomagnetic disk (or magnetoptical disk) as shown in FIG. 4 as one type of optical recording disk. More specifically in FIG. 4, a dielectric material film 52 is disposed on a substrate 51 in the form of a disk, a recording film 53 comprising a metal is disposed on the dielectric material film 52 and a protection film 54 comprising a dielectric material is disposed on the recording film 53. Further, a protection plate 58 is bonded to the protection film 54, generally through an adhesive layer 55. In addition, an outer peripheral side face of such a photomagnetic disk is filled with a filler material 57 such as resin for the purpose of protecting the recording film 53, particularly the side face thereof.
In the conventional photomagnetic disk as described above, the thin films are particularly produced according to a process as shown in FIGS. 5 and 6. More specifically as shown in FIG. 5, a mask 80 in the form of a ring is first disposed on a peripheral edge of the substrate 51 in the form of a disk which is fixed to a substrate holder 60 disposed in a bell jar (not shown) of a vacuum film formation device. An inner peripheral face 80a of the mask 80 is disposed substantially in parallel with a center line of the mask. After the mask 80 is disposed, the dielectric material film 52, the recording film 53 and the protection film 54 are laminated on the substrate 51 by a vacuum film formation (or vacuum vapor deposition) process such as sputtering, as shown in FIG. 6. Then, the mask 80 is removed and the protection plate 58 is bonded to the resultant product through the adhesive layer 55, and then the outer peripheral face of the resultant optical recording disk is filled with the filler material 57 as shown in FIG. 4.
In the structure of the above conventional optical recording disk, however, the outer peripheral face of the recording film is exposed or is only covered with a filler comprising an organic material, even if the outer peripheral face is covered. As a result, it is not sufficient to prevent the corrosion of the recording film. Accordingly, there is posed a problem such that when the optical recording disk is left standing for a long period of time, the recording film of the optical recording disk begins to be corroded from the outer peripheral portion thereof, whereby the safety or reliability of the resultant product cannot be guaranteed.